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2017 Australian Science Olympiad Exam - Chemistry

©Australian Science Innovations ABN 81731558309

CHEMISTRY

2017 Australian Science Olympiad Exam

Multiple choice answers Correct answer marked in yellow

1. Which of the following will produce a gas when reacted with hydrochloric acid?

(a) NaHCO3

(b) NaOH

(c) NaNO3

(d) Na2SO4

(e) NaH2PO4

2. Nitric oxide (NO) reacts completely with oxygen to form nitrogen dioxide according to the

following balanced chemical equation:

2 NO(g) + O2(g) → 2 NO2(g)

If 2 L of NO and 1 L of O2 are reacted in a balloon, what will be the final volume of the balloon after the

reaction is complete, assuming that the temperature and pressure are unchanged?

(a) 1.0 L

(b) 2.0 L

(c) 2.5 L

(d) 3.0 L

(e) 5.0 L

3. Calcium hydroxide (Ca(OH)2) is sparingly soluble in water, with a solubility of 1.73 g/L at 20 °C. If

0.400 g of calcium hydroxide is placed in 200 mL of water at 20°C, what mass of calcium hydroxide will

remain undissolved?

(a) 0.027 g

(b) 0.054 g

(c) 0.173 g

(d) 0.346 g

(e) 0.400 g

4. Prussian blue is a deep blue pigment containing Fe2+, Fe3+ and CN− ions. It has the formula

Fe7(CN)18. How many Fe2+ and Fe3+ ions are there per formula unit?

(a) 0 Fe2+ and 6 Fe3+



(b) 3 Fe2+ and 4 Fe3+

(c) 4 Fe2+ and 3 Fe3+

(d) 5 Fe2+ and 2 Fe3+

(e) 9 Fe2+ and 0 Fe3+

5. Element X forms compounds with two common ions: X+ and X3+. Which group is element X likely to

be in?

(a) 1

(b) 2

(c) 13

(d) 15

(e) 17

6. Why does a catalyst increase the rate of reaction?

(a) Decreases activation energy of the reaction

(b) Increases the temperature of the reactants

(c) Increases the concentration of the reactants

(d) Decreases the pressure of the system

(e) Decreases the surface area of the reactants

7. Acid number is a commonly used metric in the paint industry. It is defined as the mass (inmg) of

potassium hydroxide required to completely neutralise the acid in 1 g of paint.

A paint has an acid number of 185. What volume of 0.100 M KOH is required to completely neutralise

0.5 g of that paint?

(a) 1.65 mL

(b) 3.30 mL

(c) 16.5 mL

(d) 18.5 mL

(e) 33.0 mL

8. Phosphoric acid is a triprotic acid. What mass of Ca(OH)2 would be required to neutralise 100 mL of a

1 mol L−1 solution of phosphoric acid (H3PO4)?

(a) 3.7 g

(b) 4.9 g

(c) 7.4 g

(d) 11.1 g

(e) 22.2 g

9. Consider four elements: calcium, oxygen, potassium and sulfur. What would be the correct order if they

were arranged according to increasing electronegativity?

(a) Calcium < oxygen < potassium < sulfur

(b) Calcium < potassium < sulfur < oxygen

(c) Oxygen < sulfur < potassium < calcium

(d) Potassium < calcium < oxygen < sulfur

(e) Potassium < calcium < sulfur < oxygen



10. A diene (di-alkene) is a hydrocarbon containing two double bonds. For example,

1,3-butadiene has a double bond between the first and second carbon atoms, and another double between

the third and fourth carbon atoms. If the formula for 1,3-butadiene is C4H6,

what is the formula for 2,4-hexadiene?

(a) C6H8

(b) C6H9

(c) C6H10

(d) C6H12

(e) C6H14

11. Aqueous Fe2+ ions are readily oxidised to Fe3+ ions by oxygen gas in acidic solutions.

Consider the following relevant reduction half equations:

Fe3+(aq) + e− → Fe2+(aq)

4H+(aq) + O2(g) + 4e− → 2H2O(l)

What chemical amount (in mol) of H2O would be produced from the reaction of 2 mol of Fe2+ with

excess oxygen under acidic conditions?

(a) 1 mol

(b) 2 mol

(c) 4 mol

(d) 8 mol

(e) 16 mol



12. Excess calcium carbonate was treated with 50 mL of 5.0 M hydrochloric acid and the mass lost over 20

min recorded and plotted on the graph below. The experiment was then

repeated under changed conditions.

Which of the following could be the changed conditions?

(a) 25 mL of 5.0 M hydrochloric acid

(b) 25 mL of 10.0 M hydrochloric acid

(c) 50 mL of 2.5 M hydrochloric acid

(d) 50 mL of 10.0 M hydrochloric acid

(e) 100 mL of 2.5 M hydrochloric acid

13. Solid carbon dioxide, also known as dry ice, sublimes to form gaseous carbon dioxide. What type of

bonding is significantly weakened because of this phase change?

(a) Covalent bonding

(b) Hydrogen bonding

(c) Ionic bonding

(d) Intermolecular forces

(e) Metallic bonding

14. Which of the following elements is a solid at room temperature?

(a) H2

(b) F2

(c) Cl2

(d) Br2

(e) I2

0

1

2

3

4

5

6

0 5 10 15 20

mas

s lo

ss (

g)

time (min)

50 mL of 5.0 M hydrochloric acid

Changed conditions



15. Nitrogen dioxide (NO2) dimerises to form N2O4, as represented by the equilibrium reaction:

2 NO2(g) ⇌ N2O4(g) ∆H < 0

The following graph depicts the concentration of NO2 and N2O4 gases in a closed reaction vessel.

At t = 10 s, the equilibrium between the two species is disrupted, and a new equilibrium is reached at t

= 20. Which one of the following disruptions at t = 10 would be consistent with the graph?

(a) Addition of only N2O4 to the reaction vessel

(b) Addition of only NO2 to the reaction vessel

(c) Decrease in volume of the reaction vessel

(d) Increase in temperature inside reaction vessel

(e) Removal of only NO2 from the reaction vessel



SECTION B

ANSWER IN THE SPACES PROVIDED

Question 16

Our atmosphere is made up of 4 main gases: about 78% nitrogen gas, 21% oxygen gas, less than

1% argon, and around 0.04% carbon dioxide. Recently, a planet called TCAZlHG was discovered.

It looks similar to Eaiih and spectroscopic measurements revealed that its atmosphere consists of

the same four gases in Earth's atmosphere.

(Throughout the question, air refers to the atmosphere of planet TCAZlHG. All measurements have

been performed at the same temperature and pressure.)

A 500.0 L container filled with air weighs 23.888 kg. When the container is completely evacuated

of all air, it weighs 21.702 kg.

(a) Find the density of the air (in g L- 1) .

To detennine the percentage by mass of oxygen gas in air, an excess of copper is added to a sealed

25.00 L container filled with air. This is heated and the oxygen reacts with the copper to form

copper(II) oxide.

(b) Write a balanced chemical equation for this reaction.

(c) Calculate the mass of air in the container before the reaction occurred.

): 2S·O0LX-i\. n 2j L

= lO'l· l

1



Upon complete reaction, the mass of the remaining gas is found to be 72.40 g.

(d) Calculate the mass of oxygen gas that reacted with the copper.

(e) Calculate the percentage by mass of oxygen in the air.

(f) Calculate the mass of copper(II) oxide produced in this reaction.

MW1)= q. j-71·401

:. %·'-l,

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To determine the percentage by mass of carbon dioxide in the air, a 10.00 L sample of air is

continually bubbled through a solution of Ca(OH)z or limewater, and a white precipitate of calcium

carbonate forms, as described by the following balanced chemical equation:

Ca(OH)2(aq) + CO2(g) - CaCO3(s) + H2O(l)

Once the precipitation is complete, the solid is filtered, washed and dried, and has a mass of 11.05 g.

(g) Calculate the percentage by mass of CO2 in the air.

To find the percentage by mass ofN2 in the air, a 2.000 g sample of air is reacted with excess

oxygen and water at high temperature. Under these conditions, the CO2 and N2 form acids

according to the following equations:

CO2(g) + H2O(l) - H2CO3(aq)

2N2(g) + 3O2(g) + 2H2O(/) - 4HNO2(aq)

The resulting acidic solution is quantitatively transferred to a 250.0 mL volumetric flask and made

up to the mark. 50.00 mL of 0.1993 M NaOH is added to 20.00 mL samples of this mixture and

reacts with the acids present. Neutralisation of the excess NaOH requires 18.36 mL of 0.2101 M HCl.

The following balanced chemical equations represent the reactions of aqueous H2CO3, HNO2 and

HCl with the solution ofNaOH:

H2CO3(aq) + 2 NaOH(aq) - Na2CO3(aq) + H2O(/)

HNO2(aq) + NaOH(aq) - NaNO2(aq) + H2O(l)

HCl(aq) + NaOH(aq) - NaCl(aq) + H2O(l)

,i,o;-, lOO·O't,....t·' ::: (Hl04

/.t'\ "°l)= O·ll04 M@t):: O·ll04..J'¼•01 f11,r'= 4-·8 i j

M )= IO·OOL Y.4•372, C1

:. 4.J·12j

/o(W1)= -g q 41·72 ,I,(. l - -

tl-llZ

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©Aust rali an Science Innovations ABN 81731558309

(h) Calculate the chemical amount (in mol or mmol) of HCl added.

(i) Calculate the chemical amount (in mol or mmol) ofNaOH that reacted with H2CO3 and HNO2.

(j) Calculate the chemical amount (in mol or mmol) ofH2CO3 that will be present in a 20.00 mL

sample of the original acidic solution. (If you did not get an answer for part (g), you may assume

that the percentageby mass of carbon dioxide in the air is 10%).

n(KL\)=

=,\g

·· bM

, L

-O·2l0\ M

l\( tv OK,

f\ ( N"'O , )=

\= ;o.oJr'\L v. O·\ i1 M:: - ,;

= 6·l(lg

q,1,; -;.g57

M(U.\) =-'HOO " O·llll= O·l'lllj

" lWi=) - :;,2ct-·= s.o o

,·." :.r\(ui "' )= i o :t1'S.()50

1.U\)= ) .o

= 0•4040 .

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©Aust rali an Science Innovations ABN 81731558309

(k) Calculate the percentage by mass of N2 in the air.

t\(N"'°K, W3 \= 2."0·4040 = O·gogl

" ( NaOt<, wi,(J, HNOt) = b·iog - O·g{)gl

=. ; 300 -

" (fv)= i, s-vo ... ,-S,300 = &6•14 2·0 601C1

t : 0·O"l4. ...,,(

,n (N) = lt.·Ojl

= O·'tigt j

·• x 0·06624

o/"(N1):: 0·'\gl ( !Q-Q 4L/,, /\It

2: 000' t.'. I- "w lo

The amount fraction (also known as mole fraction) is defined as the chemical amount of a substance

in a mixture (in mol) divided by the total chemical amounts of all constituents of the mixture (in

mol).

(1) Assuming that the remaining gas in the air is argon, calculate the amount fraction of argon in the

air.

o r= lt'X>- ll·ll- 13·7, -, -4 40 = -13%

l,d, AA/': Wz. 02. , o·Hlt o,sn

(MNt) 2·S'1S- , lO

:. (A,)=

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20 I 7 Australian Science Olympiad Exam - Chemistry

©A ust ra li an Science Innovations ABN 81731558309

Question 17

The field of organic chemistry (or carbon chemistry) involves the study of how to transform organic

compounds into desired products. In organic chemistry, skeletal fonnula notation is often used to

represent carbon backbones. In this notation, bonds are represented by lines, with carbon atoms

located at the end of each line segment or meeting point ofline segments. Hydrog en atoms

connected to carbon atoms are implied rather than explicitly shown.

For example:

is equivalent to OH

Specific reactions can be us ed to transfonn one functional group (such as the OH group in the

structure above) into another. These reactions have been represented by numbers throughout this

question, as shown in the table below. For the sake of simplicity, we have also represented various

organic functional groups as letters of the alphabet from A to F (note that the letters B, C and F

refer to functional groups, not the respective elements boron, carbon and fluorine which they

usually denote). For your convenience, this table will be reproduced frequently in this question.

Reaction 1: A - C B-C

Reaction 2: A-C

Reaction 3: A-D c-B

Reaction 4: D-A Reaction 5: c-E Reaction 6: E-C

As an example, the functional group A can be converted to functional group C by either reaction 1

or 2, or to functional group D by reaction 3.

As a further example, the molecule shown on the left is converted into the molecule on the right by

reaction 3.

/A

y e B

3 ...

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©Australian Science Innovations ABN 8173 I 558309

B

(

' 8

(iii)

6,3 ...

C

3, 6..

8

Reaction 1: A ----t C B ----t C

Reaction 2: A ----t C

Reaction 3: A----tO C ----t B

Reaction 4: D ----t A

Reaction 5: C ----t E

Reaction 6: E----tC

(a) Draw the product of the following reactions. Note that when two reactions are written on the

same line they are applied sequentially from left to right, e.g. 1, 3 means do reaction 1, then

apply reaction 3 to the products of the previous reaction. Blank skeletal structures for the

products have been drawn for you.

(i)

A

1 .. (

(ii)

2 .. B

(iv)

Jyl 8

(

B

C

Pagel5of28



Reaction 1: A-----+C

B-----+C


Reaction 3: A -----+ D

C -----+ B

Reaction 4: D-----+A

Reaction 5: C-----+E

Reaction 6: E-----+C

(b) Identify the reaction step(s) required to transform the reactant on the left to the product on the

right. Note that this may require the sequential application of more than one reaction.

(i) Reaction step(s):

A

? .. D

s, C E

(ii) Reaction step(s):

A

?

• l,4 A C

(iii) Reaction step(s):

A

?

• -;, I,4- B C

(iv) Reaction step(s):

B

?

• s-, \, 3,6 C C

A

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B -----+ C


Reaction 3: A -----+ D

C -----+ B

Reaction 4: D -----+ A

Reaction 5: C-----+E

Reaction 6: E -----+ C

(c) Consider the reaction scheme below, in which the product pictured on the right is synthesised

from compound V via the reactions 3, 4, 2, 5 and then 1 respectively. None of compounds V,

W, X, Y, Z are the same as each other.

v- 3 >-w--

4 x--

2• Y-

5•-z--

1 • &:

(i) Sketch the structures of X, Y and Z. Blank skeletal structures have been provided for you.

(ii) Sketch one possible structure for V.

X y



(iii) How many different possible compounds could V be?

(d) In reaction 7, the functional groups Band C react in the following way:

C 7

B+ F

C

new bond

A new chemical bond is formed between the functional group B and the carbon adjacent to the

functional group C, and B is turned into a new functional group F in the process.

(i) Draw the product of the following reaction, and label the new bond formed.

In the following reaction, the two starting materials are mixed and reactions 3, 6 and 7 are

performed sequentially on this mixture.

(ii) Draw the product of this series ofreactions.

Page 17 of 28

6,

s + A C

7

E +

C

) "--._ 3, 6, 7



Q

One complication to a reaction such as this is that intramolecular reactions can occur, i.e. a reaction

between two functional groups on the same molecule, forming a ring. This will only occur if they

fonn 5 or 6 membered rings . Shown below is an example of an intramolecular reaction that forms a

6 membered ring with reaction 7. The atoms labelled 1 to 6 in the compound on the left correspond

to the atoms labelled 1 to 6 in the compound on the right.

C newbond

3

7 .. 2

4

(iii) Draw the product of the following reaction:

Reaction 1: A-------tC

B-------tC

Reaction 2: A-------tC

Reaction 3: A-------tD

C-------tB

Reaction 4: D-------tA

Reaction 5: C-------tE

Reaction 6: E-------tC

(iv) Suggest a series ofreactions that would transfonn the reactant on the left solely into the

product on the right.

B

A

C

C

? .. L;F c

Reaction step(s):

s,2,7,b.

C B 7

B .. F



Page I 8 of 28

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( f

(.

B

(v) Draw all potential products of the following reaction:

' 2. C 8

7

B

l

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Question 18

An important property of metallic elements is their ability to bond to one or more molecules or ions

to form metal complexes. Metal complexes may have an overall positive, negative or neutral charge

depending on the charge on the metal and which molecules or ions are bound to it. Originally, many

compounds now understood to contain metal complexes were thought of as "adducts" - compounds

consisting of two chemically distinct species in a fixed ratio. For example, C0Cb:6NH3 was thought

of as an adduct of CoCb and ammonia in a 1:6 ratio.

(a) What is the charge on the cobalt ion in CoCb?

Despite appearing to consist of two pre-existing compounds in fixed ratios, these 'adducts' show

different reactivity from their component parts. In the late 19th century, Sophus Mads 10rgensen

investigated the reactivity of CoCb:6NH3 with solutions of hydrochloric acid and silver nitrate.

(b) W1ite balanced chemical equations for the following reactions:

(i) Mixing aqueous solutions of CoCb and AgN03 (a precipitate of AgCl is one of the

products)

(ii) Mixing ammonia with hydrochloric acid.

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I \ H H H

It was discovered that one mole of C0Cb:6NH3 reacted with 3 moles of AgN03, however there was

no reaction with hydrochloric acid. 10rgensen proposed that these observations suggested that the

ammonia molecules were bonded in such a way as to be unreactive. He suggested the following

structure, claiming that ammonia could fonn linear chains similar to -CH2- units in hydrocarbon

chains: H H

c,i... \ /

H H H H ---H Cl"- / H\ \N/ I Co Cl

N / - N- "- / H// - N \ N- H

I-I / \ HHH /\

H

J0rgensen formulated this structure well before modem theories of valence and bonding like Lewis

structures had been developed.

(iii) Draw a Lewis (or electron dot) structure for ammonia

(iv) Suggest why the structure of C0Cb:6NH3 is unlikely to consist of these ammonia

chains.

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Nevertheless, 10rgensen's structure was consistent with the experimental evidence available at the

time. Other adducts of the form CoCb:xNH3 were discovered, and their properties are summarised

in the following table:

Composition Colour Amount of AgNO3 (mol) required for complete reaction per mole of adduct

C0Cb:6NH3 Orange 3

C0Cb :SN H3 Pink 2

CoCb:4NH3 Green 1

CoCb:3NH3 Violet 0

To explain the fact that one of the chlorine atoms in C0Cb:SNH3 did not react with silver nitrate,

10rgensen proposed the following structure, in which the "unreactive" or "masked" chlorine is

bonded directly to the metal: CI

H / H

. \

H H H H 7-.H c, i I ---\--{_- Co"

-----N- N \ I\ Cl H / /\ H H H

H H H

(c) Draw a structure for CoCb:4NH3 that would, according to 10rgensen's theory, explain its

observed reactivity with silver nitrate.

Unfortunately, 10rgensen's theory starts to break down when we consider CoCb:3NH3. forgensen

proposed the following structure, in which the ammonia chain is shortened by one:

H H H Cl

H \ / I / \ N- N_Co "-

Cl- N/ \ /\ Cl I\ H H H H H

(d) Explain why forgensen's structure does not agree with the experimental results above.

N.

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Alfred Werner conducted experiments with the same series of compounds, measuring their molar

conductivities in solution (higher numbers mean greater conductivity per mole of compound

dissolved). From this he reasoned that these compounds must dissociate into different numbers of

ions in aqueous solution. Werner's data is shown in the table below:

Composition Molar conductivity Number of ions present per fonnula unit

C0Ch:6NH3 431.6 4

C0Ch:SNH3 296.4 3

CoCh:4NH3 98.35 2

CoCh:3NH3 ? ?

(e) Explain the relationship between the conductivity of a solution and number of ions present.

(f) Notice that the data is missing for CoCb:3NH3

(i) Predict the number of ions present in CoCh:3NH3.

(ii) Hence, predict the molar conductivity of CoCb:3NH3.

To rationalise both his conductivity data and J0rgensen's data, Werner proposed that 3 of the 4 ions

in C0Ch:6NH3 correspond to c1- ions, which would therefore be able to react with silver nitrate.

According to Werner's theory, the ammonia and the cobalt formed a single 'complex' ion:

[Co(NH 3)6]3+ . Thus, it would be more appropriate to write the ionic formula for C0Ch:6NH3 as

[Co(NH3)6]Ch.

According to Werner's theory, C0Cb:SNH3 would consist of two c1- ions and the complex ion

[C0Cl(NH3)s]2+ . Werner suggested that this explained 10rgensen's observations, as only the two

ionic chlorides could react with silver nitrate, while the chloride that is directly bonded to the cobalt

would not react.

0

0

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0 '--'

....

(h) Write the fonnula of the complex ion in CoCb :4NH3. Does this formula agree with fa rgensen ' s

silver nitrate observations and Werner' s conductivity data? Explain you answer.

Werner conducted further experiments with other adducts and found that he could use his model of

metal complexes to explain their physical and chemical properties. The following table and graph

summarise the conductivity and reactivity with AgNO3 of a series of adducts of the form

PtCh:xNH3. It is known that these compounds contain Pt2+ .

Composition Amount of AgNO3 (mol) required for complete reaction per mole of adduct

PtCh:4NH3 2

PtCh:3NH3 1

PtCh:2NH3 0

PtCh:NH3:KCl 0

A 0

300

250

,.-.._

8 ..c: 200

.>...-

: c..l :::l

":O:::

0

150

(.) 100

r1-o..

0 :B

so

0

PtC12·4NH 3 PtC12·2NH 3 A

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(i) Use the data above to answer the following questions . You will need to use similar reasoning to

that outlined in the earlier parts of the question.

(i) Write formulae for PtCh:4NH3, PtCb:3NH3, and PtCh:2NH3 that reflect the fact that they

contain complex ions.

(ii) The concept of coordination number refers to the number of molecules or ions directly

bonded to the metal centre. For example , the ion [C0Cl(NH3)s] 2+ has a coordination

number of 6. What is the coordination number of this series of platinum complexes?

4- (iii) Based on the trend in the first three compounds, and considering the experimental data

predict the formula of the complex ion in PtCh :NH3:KC l.

(iv) Predict the formula for A given that it contains potassium, chlorine and a Pt+2

with the same coordination number as in part (ii), but contains no ammonia.

ion

f ( li.:4k'H1= ft lNH, 1t Cl1

Pt Cl,.: NHl:::: [ fU l(NH3h ]C I

ft (l 2

2."'1Hi= t ((i(N 1),]

[Pl(l,(llHJ)]

KLPt ( l\(NH,TI

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Boiling a solution of PtCh in ethanol followed by the addition of potassium chloride produces

yellow crystals of a substance first isolated in the early 19th century. These yellow crystals react

vigorously with both oxygen gas and hydrogen gas but not with silver nitrate. At the time of its

discovery, elemental analysis was not possible for all elements but the following percentage

composition by mass data was found: Pt 50.46%, Cl 27.51%, C 6.21% 0 4.14%, H 1.56%. Later

studies showed that the Pt2+ ion also has the same coordination number as in part (ii).

(v) Predict the formula for these yellow crystals.

0 H ili.. J.il

0·11{,

lb·OO - l oog

-0 2.sq l '\

MM, : - ( O·ltb '2.1·Sl?b·21+4·14-t-l•%)= W·l2

\ 3 l {,

M n(!<\ == W:,:: 0·2S'l.

=K

:. \( {Gl\LJ-{,O.

K[f ll,,(Ci OH)l

t<.L U,llt )}u,.o -Utt

OJJ!ltf Hi:

ola..Jut .

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